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Nt46xp

9 Posts

Posted - 07/14/2010 :  09:56:22 AM  Show Profile  Reply with Quote
Getting a buzz inside at compressor or fan motor when thermostat calls for cooling. Would there be a chance that starter capacitor or relay is bad?
If not are there any serviceable parts associated with electrical for compressor?

Edited by - Nt46xp on 07/14/2010 10:06:32 AM

Cozy.Support

5709 Posts

Posted - 07/14/2010 :  3:59:26 PM  Show Profile  Reply with Quote
A faint buzz with neither the fan motor or compressor running could mean a lot of things. First thing is to check all breakers and fuses for the outdoor unit.

All of the starting components should be available if you determine that you have defective components.



CozyParts.com, Inc. is an Independent Lennox Dealer providing a national parts distribution resource for Lennox parts since 2002. The Cozy.Support team does not provide a diagnosis for users of this forum. We do, however, try to provide information that will help servicers arrive at their own diagnosis.

Once you know what part you need, you can contact the Cozy parts department by using the link below
http://www.cozyparts.com/Lennox-Parts/locator_form.aspx
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Nt46xp

9 Posts

Posted - 07/14/2010 :  4:51:29 PM  Show Profile  Reply with Quote
I have 240v across the terminals at the relay, so was thinking the supply was good. The buzz might be coming from a transformer on side of compressor (and it seems to cycle a little from a soft buzz to a little louder buzz and back to soft buzz. The compressor and fan do not come on. From other posts was thinking maybe the big cap on the from in was bad so fan and compressor not getting enough energy to start up, but didnt want to willynilly start buying parts to try (cap is like $50). If it was $10 it would be on order already. We have had some strong storms a few weeks ago so another post suggested that maybe cap got friend from surge.
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MechAcc

1499 Posts

Posted - 07/15/2010 :  07:13:54 AM  Show Profile  Reply with Quote
It might be dirt under the contactor armature. Get a can of compressed air turn the thermostat off and remove the power to the condensing unit by pulling the disconnect. Then blow air through the contactor sides and under the contacts.

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have all of your fossil fuel appliances tested annually for carbon monoxide production by a professional.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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Nt46xp

9 Posts

Posted - 07/15/2010 :  10:21:20 AM  Show Profile  Reply with Quote
Used compressed air to blow off contacts and tried restart and got same result. Upon closer inspection the contacts were not smooth so tried to jumper across while contact was engaged (during start up). No change.
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MechAcc

1499 Posts

Posted - 07/15/2010 :  10:41:08 AM  Show Profile  Reply with Quote
If the contactor is indeed what is buzzing check and make sure that 24vac is being applied to the coil and is not below 20 volts. When a lower voltage is applied to the coil it becomes harder for armature on the contactor to fully pull in. If the voltage is 24 vac or higher then get a new contactor.

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have all of your fossil fuel appliances tested annually for carbon monoxide production by a professional.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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Nt46xp

9 Posts

Posted - 07/15/2010 :  11:02:04 AM  Show Profile  Reply with Quote
Thanks for the info. Just want to make sure we are talking the same thing. On the input side of the unit there is a relay (I guess). When there is power and thermostat calls for cooling contact closes and appears to apply power to the fan and compressor. It is this relay that I cleaned and jumped the contacts on, the transformer that is buzzing is inside at the base of the compressor. Are we talking the same thing? Is the 24vac coming off the transformer on the input or the transformer on the compressor?
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slctech

2085 Posts

Posted - 07/15/2010 :  11:07:20 AM  Show Profile  Reply with Quote
From the drawings of this unit it looks like this has a suicide contactor/relay factory installed. What I mean by this is that one leg of the incoming power is continuously running straight through the contactor/relay while the other leg is actually has the actuator that would be pulled down to allow power to start-up the equipment.

You say you bypassed the relay and the unit still did not operate? When the thermostat is calling for cooling is can you actually see the contactor/relay's armature actually pulled down to make contact on the relay?

Most contactors have the incoming side marked T1 and T2 and the outgoing side to the equipment marked L1 and L2...check these voltage readings when the thermostat is calling for COOL.
T1 to Ground (body or ground wire inside the unit)
T2 to Ground
L1 to Ground
L2 to Ground
T1 to L1
T2 to T2

Make note of these voltages and let me know what you got. This will help tremendously in seeing what is going on here.

I have a feeling you lost one of the legs of voltage...you may have bus fuses in the outdoor disconnect box, if so check that they are both good and have continuity through them. Also check the interior of the disconnect that there are not any burned or loose wires that may have caused one of the power legs feeding your unit to lose power.

As a Lennox Technician I feel basic repairs and maintenance can be performed by the homeowner. But I highly suggest that periodic maintenance should be made by a certified licensed technician. You should contact your local Lennox technician for any repairs or issues that are outside your comfort zone. Property damage, personal injury, and death can occur from improperly repaired or maintained systems. Replacing a part doesn't always resolve the issue that caused the part to fail!
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Nt46xp

9 Posts

Posted - 07/15/2010 :  3:42:31 PM  Show Profile  Reply with Quote
You are correct on the suicide contactor/relay, that is how it is configured.
On the disconnect front, there are no fuses, just a pull out block with straight thru jumpers.
When calling for cooling the armature moves to close the contact.
T1 to ground 120vac
T2 to ground 120vac
L1 to ground 120vac
L2 to ground 120vac
On the L1 and L2 wasnt sure which output you were referring too. So L1 and L2 are the straight thru leg of commercial power and the switched leg of commercial power.
T1 to L1 0vac
T2 to L2 0vac
So I checked what looked to be like the other outputs on side (secondary side of transformer?)
Blue wire to ground 0vac
Yellow wire to ground 24vac
Interior of the disconnect seems to be all good.
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Nt46xp

9 Posts

Posted - 07/15/2010 :  3:48:15 PM  Show Profile  Reply with Quote
Think I have it backwards the 24v is coming from the furnace/thermostat, 24v is pulling the armature to pass the 2 power legs.
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MechAcc

1499 Posts

Posted - 07/15/2010 :  4:33:11 PM  Show Profile  Reply with Quote
If the L-1 to L-2 measurement is zero volts then you have lost a leg. Are there fuses installed? Check them. The contactor coil voltage should be checked in an out. If you do not have 24 vac this way but you do with one test probe to ground you may not have a complete electrical circuit.


Also please list the model number as some units have resettable high pressure cutout switches and some do not.

I am not an employee of CozyParts. The opinions that I post are my own.

Please have your furnace inspected annually by a qualified service technician. Have all of your fossil fuel appliances tested annually for carbon monoxide production by a professional.

Get a good Carbon Monoxide Alarm. Replace it according to manufacturers recommendations usually every 3-5 years. CO concerns are not just for the winter but 24-7. UL approved alarms alarm high. For a low level alarm do a search for CO Experts or NSI 3000 a low level CO monitor.
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Nt46xp

9 Posts

Posted - 07/15/2010 :  5:41:04 PM  Show Profile  Reply with Quote
With cooling demand, L1 to L2 is 240vac (same as T1 to T2). No fuses that I can see on the input side.
Model number HS18-211-8P

Edited by - Nt46xp on 07/15/2010 5:42:34 PM
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Nt46xp

9 Posts

Posted - 07/19/2010 :  5:07:47 PM  Show Profile  Reply with Quote
How do I test the capacitor?
Could the cap be the problem with the motors not starting?
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